This invention relates to a sealing device for an air rotary joint which supplies compressed air to pneumatic operated equipment such as an air clutch etc.
A conventional apparatus of the type to which the air rotary joint of the present invention is directed is illustrated by FIG. 2.
In FIG. 2 showing an automobile air clutch which is a kind of pneumatic equipment, 10 is an engine side flywheel. A clutch cover 12 is fastened to the flywheel 10 and a pressing force generated by an annular pneumatic actuator 14 (pneumatic equipment) of the clutch cover 12 is exerted on a pressure plate 16, so that a clutch disc 18 is held between the pressure plate 16 and the flywheel 10.
The clutch disc 18 is spline fitted onto an input shaft 20 of a transmission (not shown) disposed at a rear stage of the air clutch. A cylindrical shaft 24 is fitted onto an outer periphery of the input shaft 20 through a bush 22. The clutch cover 12 fits onto a left end portion in the figure of the cylindrical shaft 24.
A right end portion of the cylindrical shaft 24 is surrounded by a cover 26, and a chamber 28 is formed in an inside of the cover 26. Three air seals 30a through 30c are disposed between the cover 26 and the cylindrical shaft 24 so that air leakage is prevented by the air seals 30a.about.30c as described later in details.
On the other hand, a control valve 32 operated by a clutch pedal 31 is pneumatically connected to the cover 26, and compressed air flowing from a compressor 34 through a pressure regulating valve 36 to the control valve 32 is controlled thereat to be sent to a passage 42 through a chamber 38 between the air seals 30a and 30b and an inlet port 40 of the cylindrical shaft 24. Further, a left end portion of the passage 42 opens to an outlet port 44, and the outlet port 44 is connected through a passage 46 formed in a thickness of the cover 12 to an air chamber 48 of the pneumatic actuator 14.
In this structure, however; a peripheral speed of a lip increases at a time of high speed rotation and a pressing force of the lip increases due to an increasing tendency of pneumatic pressure, so that a PV-valve (P: pressure and V: peripheral speed) increases to finally induce a danger of a breakage of the air seal due to frictional heat.
In this connection, the applicant of the present invention has previously attempted to improve the prior art air rotary joint shown by FIG. 2 by forming a lubricating oil chamber at an outside of the air chamber 35 by combining plural air seals. However, this prior attempt provides an imperfect solution in that air leaks from the air chamber 38 to the lubricating oil when the engine is stopped.